Science and technology

Energy storage

Difference Engine: Air apparent

DESPITE their excellent fuel economy, squeaky-clean exhausts and generous government subsidies, electric vehicles have failed to catch on with the motoring public. Fewer than 10,000 pure electrics (less than 0.1% of new-car sales) trickled onto the roads of America in 2012. And that was their best year ever.

Customers continue to be put off by a not unreasonable fear of being stranded by the roadside when the vehicle’s battery pack goes flat, miles from home or the nearest recharging station. Fully charged, pure electrics have a range of typically 75 miles (120km) or so—though Tesla’s $90,000 top-of-the-range Model S, with its 85 kilowatt-hour battery, can officially clock 265 miles on a single charge.

Hybrid cars are a different matter. Having a petrol engine coupled to an electric motor (or two) allows them to recharge their batteries while on the move. Regenerative brakes help the engine-driven generator keep the battery topped up. Their freedom from “range anxiety” has made hybrids like the Toyota Prius a popular choice, especially in California where they enjoy additional subsidies and benefits on the freeways.

Lacking the ability to recharge themselves puts electric vehicles at the mercy of their battery capacity. Invariably, that is a trade-off between weight and cost. In terms of energy density, the most popular battery technology to emerge over the past 20 years is the powerful but temperamental lithium-ion cell—in the news lately for causing fires on board Boeing’s latest passenger jet, the 787 Dreamliner. All 50 Dreamliners currently in service have been grounded as a result, and deliveries of new aircraft halted while air-safety experts try to fathom the cause of the lithium-ion battery fires (see "Difference Engine: An innovation too far", January 28th).

Theory suggests lithium-ion cells should be able to store a little over 400 watt-hours of energy per kilogram. They currently pack about half that and cost around $500 per kilowatt-hour of capacity. A pure electric car like the Nissan Leaf needs 24 kilowatt-hours of electrical storage to travel 75 miles or so on a single charge. That suggests its lithium-ion battery costs around $12,000—in other words, about 40% of the vehicle’s price before tax breaks.

To rid themselves of range anxiety, electric cars need batteries three or four times better. In an ideal world, they would store as much energy per kilogram as the hydrocarbon fuel used in a conventional car. The energy density of petrol is approximately 13 kilowatt-hours per kilogram. After accounting for all the losses in the engine and driveline, the energy available at the wheels for propelling a petrol-engined car is typically no more than 1.7 kilowatt-hours per kilogram of fuel.

As the numbers indicate, the lithium-ion battery—at least in its present form—cannot compete. Some battery researchers believe there are gains still to be had from lithium-ion chemistry. May be. But many are sceptical about claims that a doubling of the cell’s energy density and a halving of its cost is feasible.

But even if the sceptics are proved wrong, a lithium-ion battery offering twice the range would still fall well short of petrol’s performance. And electric-car owners would continue to suffer from range anxiety, even more so than ordinary motorists facing a fuel gauge showing a tank almost empty: the nearest petrol station is usually just a mile or two away; recharging stations for electric vehicles are far fewer and farther apart. At least for electric vehicles, then, lithium-ion would seem to have reached the end of the road.

The only battery technology that comes close to matching the energy density of petrol is lithium-ion’s close cousin, the perpetually promising lithium-air cell. In theory, at least, this can deliver up to 12 kilowatt-hours per kilogram.

Even if only half that were ever achieved commercially, it is not unreasonable to expect something like 1.7 kilowatt-hours per kilogram to be available at an electric vehicle’s driven wheels—given the far greater efficiency of electric motors and their transmission systems. In a “well-to-wheels” comparison, the overall efficiency of an electric vehicle (25%) is twice that of a car powered by an internal combustion engine (12%). The electric vehicle is arguably cleaner, too.

Long before Sony introduced the first commercial lithium-ion battery in 1991, lithium-air was being touted as ideal for electric vehicles. That was back in the 1970s, following the first of the oil shocks that tripled petroleum prices and sent carmakers scurrying for alternative fuels and better energy-storage systems.

It took less than 20 years for lithium-ion, despite its thermal instability problems, to go from powering laptops, phones and other portable devices, to becoming the leading contender for heavy-duty applications such as electric vehicles, plug-in hybrids and even aircraft. So why has it taken twice as long for lithium-air—an even lighter and more powerful storage technology—to make it barely out of the laboratory?

The short answer is the difficulty in building lithium-air cells that can be recharged thousands of times. While the battery in a mobile phone is expected to last no more than two to three years (say, 1,000 recharging cycles at most) before the phone is tossed for a later model, motorists expect electric vehicles to come with at least 100,000-mile warranties on their batteries (say, 3,000 recharging cycles at the very least).

If maintained properly, lithium-ion batteries can manage that without too much difficulty. As they stand, lithium-air batteries cannot. After 40 years of development, the life of rechargeable lithium-air cells tends to be measured at best in terms of a few hundred, rather than several thousand, charging cycles.

The key to lithium-air’s high energy density is the way it dispenses with the heavy metal cathode of its lithium-ion cousin, and uses instead a lightweight porous electrode made of carbon that breathes oxygen from the air. On discharge, an electrolyte grabs positively charged lithium ions from the anode and transports them to the cathode, where they combine with the oxygen to form lithium peroxide. Meanwhile, electrons flow in an external circuit from the anode to the cathode, powering an electric motor or other equipment on the way.

Though theory says it should, the lithium peroxide is reluctant to do the reverse (replate the anode with lithium metal and return the borrowed oxygen to the air) when a current is applied externally—ie, when charging, rather than discharging, the cell. Why that should be so has stumped researchers for decades, and is one of the reasons why lithium-air has failed to fulfill its promise.

Lately, however, unsuspected reactions have been detected between the lithium ions and the electrolyte as well as with the carbon in the cathode. Such clues have helped researchers choose different electrolytes, membranes and electrode materials that promise to endow lithium-air batteries with far longer recharging lives.

No question there has been as much hype as hope among lithium-air’s hard-core supporters. But those championing rival chemistries—including zinc-air as well as lithium-ion—have been guilty of belittling lithium-air’s genuine advances, while making pie-in-the-sky promises of their own.

Inevitably, the back-biting is all about money for research—especially from the ARPA-E programme established recently by the Department of Energy (DoE). Endowed with $400m of economic-stimulus money, ARPA-E is a clone of the Pentagon’s hugely successful Defence Advanced Research Projects Agency (DARPA). For over half a century, DARPA has made a name for itself by backing bold ideas facing entrenched opposition and long gestation periods. The internet was one of the agency’s early successes. The F-117 stealth fighter was another.

Last November ARPA-E announced some 66 grants worth a total of $130m for “transformational” changes in energy research. The largest award, amounting to $4.5m, went to PolyPlus Battery Company, a 30-person firm in Berkeley, California, that spun out of Lawrence Berkeley National Laboratory in the 1990s. Earlier last year PolyPlus also won a $9m grant from the DoE’s Advanced Manufacturing Office, to build a pilot line for making its special “protected lithium electrodes”. The process encases the lithium anode with a ceramic membrane that allows lithium ions to pass through but is impervious to liquids or gases.

Protecting the lithium electrode this way changes everything. For a start, it allows freer use of aqueous electrolytes. Normally, water is the last thing that should be allowed near lithium. As readers may recall from their school chemistry class, the metal ignites on contact and burns furiously. For decades, non-aqueous electrolytes (mainly carbonates, ethers, esters and other organic compounds) were used in lithium batteries for that very reason. Lack of an efficient electrolyte has been another reason for lithium-air's slow development.

The protection technology has even made it possible to use seawater instead of air as a source of oxygen—like the gills of a fish. With an eye on the marine market, PolyPlus has already built a lithium-seawater battery that puts out 1,300 watt-hours per kilogram—three times more than lithium-ion’s theoretical maximum. The company’s long-term goal is to use this know-how to advance its own lithium-air system. PolyPlus’s first commercial applications are destined for consumer electronics. Later, when the the number of recharging cycles is high enough, the plan is to tackle the electric-vehicle market.

PolyPlus will not be alone. Last month, Toyota agreed to share its battery know-how with BMW, in exchange for a steady supply of modern diesel engines from 2014 onwards. The collaboration includes the development of an advanced lithium-air battery as well as a new fuel-cell for vehicles Toyota plans to start selling in 2015.

Meanwhile, IBM’s Battery 500 Project, launched in 2009 at the company’s Almaden research laboratory in San Jose, California, aims to develop a lithium-air battery capable of propelling a car 500 miles on a single charge. Like PolyPlus, much of the research has focused on finding the most appropriate electrolyte and developing a membrane that can filter pure, dry oxygen from the atmosphere.

IBM is not doing this out of idle curiosity. Like everyone else bidding for a piece of the business, it truly believes there will be a seriously large market for advanced traction batteries once they have the storage density to rival petrol and are capable of providing years of trouble-free motoring. When will that be? The consensus is early in the next decade.

You give details but I think most readers will fail to understand what is going on here - Li-Air (O) works at approaching (albeit still not reaching) petrol engine density because they are basically burning Li as a fuel and keeping the oxide on-board - reducing it back to metal to charge. In this respect they are quite like some Hydrogen systems. The big gain is from not carrying the Oxygen (all the time - note that the battery gets much heavier as it discharges). Because Oxygen is very heavy the gain from not carrying it is great.

On the other hand it is still inferior to a good hybrid - so what is the point? It only reduces Carbon emissions if you use non-carbon-releasing sources such as nuclear for electricity generation. Meanwhile it looks good to car manufacturers because it helps to claim (probably unjustified) green credentials.

If it wins in the marketplace fine - but let us stop subsidising these doubtfully-helpful technologies!

Drivers are "put off by a not unreasonable fear of being stranded by the roadside when the vehicle’s battery pack goes flat, miles from home or the nearest recharging station"?

Because if your petrol or diesel engined car runs out of fuel "miles from home or the nearest [filling] station", that's much easier to deal with, right? You walk, jerry-can in hand, hoping to thumb a lift…

Look, if you use your car to drive to work and home again, less than 45km each way, you could charge it overnight and never notice the difference between that and filling up at the pump once every two weeks.

I think we've done this discussion to death, here on the Economist and elsewhere. People avoid electric cars because they are unfamiliar and for the moment untested and unaffordable compared to petrol and diesel models.

Yes, or if that long trip is infrequent then renting a car for a few days is probably more economic than owning a second car…

For years, our household had either no car or only one car.

You're right, that "consumer like the choice of been able to make with their car". There is the whole crux of the matter, and one I've seen first hand: people will buy the very biggest vehicle that they can barely afford to run, in order to be able to drive to the store and bring home a sofa once every ten years or to bring home a 72 inch TV screen once every five years.

AS I WROTE ALMOST 20 YEARS AGO
The tree huggers, politically correct bureaucrats and politicians want the industry to offer us “zero emission” cars, at gunpoint if necessary. This is one of those save-the-world proposals that does not have a snowball’s chance of succeeding.
First, electricity is not free, you have to make it, and that means fossil fuels, because those same tree huggers already stopped us from building safe, clean, fission power plants. Instead they have us chase such chimera as hydrogen, solar power (economical only for isolated locations), and fusion (unproven except for nanoseconds), but I digress. Every highway vehicle not tethered to a fixed route must carry it’s own energy supply. We operate in an oxygen atmosphere therefore the vehicle need not carry its oxidizer, only the fuel. This is fortunate, because the typical reaction involves 16 pounds of oxidizer for every pound of fuel! Excuse me, 16 politically correct grams of oxidizer for every politically correct gram of fuel. A zero emission vehicles (ZEV) unfortunately, must carry not only the equivalent of 100 pounds of fuel to make a reasonable trip, but also the 1600 pounds of oxidizer (or other reagent) to react with the fuel, which they then can convert to 1700 pounds of reaction product to carry back to the recharging station.
Now, modern engines are about 25% efficient (35% if they are diesel). The zero emission vehicle since it needs to carry 17 times as much propellant, (fuel plus oxidizer) must be at least 17 times as efficient to compete. Let’s see, 17 times 25% is 425%. That is to say for every kilowatt-hour used to charge the battery the motor must be able to do over 4 kilo-watt hours of work. Am I missing something here? No, I'm not.
I was explaining this to an electrical engineer. He stopped me, momentarily, with “I’m not convinced the same limitations apply.” He was sort of right. In practice, ZEV is even less practical. It takes a thousand pound battery pack to store as much energy as four pounds of gasoline, and it has to carry those 1,000 pounds all the time. (Not yet 17:1, but so far only 200:1)
For the ZEV to hope to compete, it must have a propulsion system that can put out four times as much energy as what we put in. If we could do that, it could charge its own batteries and would never have to recharge, perpetual motion. Not only that, but we could use that technology to build power plants that put out four times more power than the fuel they use. We could then cascade these, each one driving one four times as big and we could power North America with a single candle. Better yet we could just tap a candle’s worth off anywhere in the system to power it. Wow! I hope you see I’m being facetious.
Meanwhile back here on planet Earth, the best fossil fuel power plant is about 42% efficient, so to get that one kilowatt we had to burn the equivalent of 2.3 kilowatts of fuel. Even if the ZEV were perfect, 100% efficient that kilowatt-hour of stored energy would weigh 17 times as much as a kilowatt-hour of stored fuel. So it could compete with engines that were 6% efficient. Look out James Watt, the original one, 1736-1819, steam engine, teakettle, you know.
It would obviously be more productive to look for a way to take the reaction products out of the air, than to attempt to carry them around and reprocess them. We could have huge un-power plants that take carbon dioxide out of the air. Plants that absorb carbon dioxide from the air and turn it into something useful, like, umm... wood.
“Hydrogen,” I hear you crying, “hydrogen is the fuel of the future. Fuel cells can turn hydrogen directly into electricity and the byproduct is pure water. Hydrogen is the answer, not batteries, not only that, but hydrogen is the most abundant element in the universe, we’ll never run out.”
Here’s a buck, go buy me some. Sure it’s abundant, but it’s all being used. Most of it is busy being water. The rest is tied up in organic compounds, such as, uh, oil. Just like electricity, before you can buy hydrogen someone has to make it and making hydrogen requires … electricity. Yes, hydrogen is the fuel of the future, and it is every bit as promising today as it was 30 years ago.

From minor inaccuracies about li-ion batteries causing the Boeing fires (it was actually faulty wiring) to more significant ignorance on the current state of the hybrid/EV industry, this piece misses the mark on the big picture of EV development.

Pure electrics are only just starting to hit the mainstream auto markets. Once relegated to university science projects, cars like the Nissan Leaf are still in their infancy and expectations of direct competition with say, Honda Civics, are completely unrealistic. Nobody is expecting that first generations pure EVs will be instantly competitive on issues like range. That being said, strong growth remains a key hallmark of the EV industry and hybrid offerings are maintaining a popular bridge to the eventual competitive, all-electric market.

A few facts to consider:

- More than 487,480 electric drive vehicles – hybrids, extended range and battery – were purchased in the U.S. in 2012. (Source: Electric Drive Transportation Association)

- Research from Mintel states that sales of hybrid and electric vehicles rose 73% in 2012, “making it the fastest growing segment in the U.S. auto market”

- The Chevy Volt was the number one-ranked car in Consumer Reports’ consumer satisfaction survey for the second year in a row. (Source: Consumer Reports)

- The all-electric Tesla Model S was named Motor Trend’s Car of the Year for 2013. Motor Trend praised the car, calling it “a truly remarkable automobile” and “one of the quickest American four-doors ever built.” As for the electric drivetrain? Motor Trend concludes, “at its core, the Tesla Model S is simply a damned good car you happen to plug in to refuel.” (Source: Motor Trend Magazine)

- Nissan – world’s largest seller of electric vehicles – is upgrading the Leaf for 2013. All 2013 Leaf models have improved electric range, and recharge time for SV and SL grades falls to four hours from a 220-volt outlet, from about seven hours currently. Nissan is also adding a cheaper, entry level Leaf to boost sales, after Leaf deliveries to the U.S. rose 1.5% in 2012. (Source: Bloomberg News)

- The Telsa Model S is capable of travelling 250 miles per charge. (That’s Boston to New York with roughly 50 miles to spare.) For reference, in 2009 the average American traveled 28.97 miles in a vehicle per day. (Source: Green Car Congress and U.S. Department of Transportation)

While the Economist does well to explore the future of lithium ion battery tech, this piece does not do justice to the growth in the industry, nor the efforts of technology leaders like IBM who, as is mentioned in passing, clearly see promise in future EV tech.

For more facts on the ongoing development of EVs and other renewable energy technologies, check out http://energyfactcheck.org and follow on Twitter at @EnergyFactCheck

As an owner of one of these expensive Tesla Model S's I can say that the ONLY barrier to this car is the price. Range of 400km (300km in winter) satisfies 100% of my driving needs without ever charging not at home. Every morning I leave with a full 'tank'. If you are looking at a car in this price range I have no idea why you would not consider the Tesla - inherently reliable, wow performance and technical wizardry in one package. The cost of batteries needs to come down more that the energy density needs go up (although both are happening incrementally). Simply an amazing car.

No, actually not. In the late 1800s, nobody even understood the structure of an atom, much less the concept of a band gap. The galena and "cat's whisker" diode was a mystery empirically stumbled upon. In the early days of radio, there were some sporadic attempts to try to understand it, and there is some evidence that at some point someone may have even accidentally produced something like a transistor effect when putting a "probe" cat's whisker near the active one, but whatever it was was transient and not reproducible.

The post-war work at Bell Labs that led to the development of the transistor was initiated as an attempt to understand how solid-state diodes worked. The old crystal diode had been improved with better manufacturing techniques into a sturdy packaged component, but still nobody really know how it worked. Likewise, while "semiconductors" in the form of copper oxide and later selenium rectifiers were being used in battery chargers, the physics was still fairly mysterious. The transistor itself, of course, was discovered rather than invented, when an unexpected amplification effect was observed when two cat's whiskers were placed nearby on a single crystal.

Materials science was vital, but until the transistor effect was discovered, nobody even knew that ultra-pure germanium, and later silicon, would ever be needed. Once there was a physicist to tell the chemists that he needed a semiconductor with a purity on the order of 10^-13, the chemists and manufacturing engineers could set about trying to make it, but in the 1800s nobody would have even had a clue that such a material could be of any particular use.

Even the vacuum diode wasn't really invented until the 20th century, and that, rather like the transistor, was an accidental result based on an empirical observation -- in that case, an attempt to figure out how to keep light bulbs from burning out so fast. The step from the diode (rectifier) to the triode (amplifier) represented yet another accident -- in that case an attempt to understand what was going on between the anode and cathode in a diode.

Nearly all of the great technological leaps are the result of lucky discoveries and an open mind, rather than directed research.

Current electric vehicles do not necessarily shift polution elsewhere. I have signed up for 100% wind-power sourced electricity at my house, so if I did all my charging there, you could still reasonably claim very low to no emissions. Additionally, there are benefits to "shifting" that polution elsewhere: A natural gas-fired electricity plant that operates at 85% efficiency is far better than burning gasoline locally at 25% efficiency. Best yet, though, would be a fuel-cell powered local generator at my house, but for now charging the cars using low emissions electricity sources is the best we can hope for.

I think the electric car concept is exciting, but it needs substantial amount of time to become mainstream or at the most close competitor to gasoline engine driven cars. Secondly, US is such a big country and there needs to be in place sufficient infrastructure to support drivability of electric vehicles. The situation is different in Europe, where there are more densely packed towns than in the US and setting up charging stations would be easier.
I had the opportunity to chat with one of Tesla's employees, and he rightly said there are more people buying tesla cars in Norway and other scandinavian countries than in the US. Does this reflect the mindset of the people living in those countries and how much they care about protecting their environment?

While the battery in a mobile phone is expected to last no more than two to three years (say, 1,000 recharging cycles at most) before the phone is tossed for a later model, motorists expect electric vehicles to come with at least 100,000-mile warranties on their batteries (say, 3,000 recharging cycles at the very least).
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That's only because of managed expectations.
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Mobile phones are basically "leased" for 2 years, as consumers know they will have to upgrade in 2 years in order to keep up with whatever technological "innovation" has occurred.
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As more and more go from outright purchasing of vehicles to leasing for a short periods of time, then a battery that lasts a year longer than the lease can be used. (ex: 3 year battery life for a 2 year auto lease.)
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NPWFTL
Regards

Not every engineering problem can be solved. It may be that full electrics will never be successful highway vehicles. But consider all the urban applications that can eliminate emissions at their most concentrated and obnoxious.
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But the competition from natural gas is severe.

Use of the phrase “squeaky-clean exhausts” can be very misleading. Batteries do not produce any energy. Like gas tanks they are storage containers that consume energy and produce Green House Gases (GHG) by manufacturing them. The sun doesn’t discriminate by location of tail pipes. The EPA measures emissions of the U.S. electricity grid at 1.6 pounds of carbon dioxide per kilowatt hour. When line losses and AC/DC charger conversion efficiencies are considered the real number is about 1.8 lbs/kWh. Assuming the EPA Tesla-S rating of 35 kWh per 100 miles; driving the car from a grid connected charge station to the next one produces 70% more carbon dioxide per mile than a Prius Hybrid. So why would anyone drive a rechargeable electric beyond the range of renewable fuel powered charge stations? Does the thrill of acceleration outweigh the life expectancy of grandchildren? Or is saving a few hundred dollars in fuel cost with a $90,000 (before subsidy costs) car the motivator? Imagine the alternative benefits of powering a $25,000 hybrid with natural gas or saving the equivalent of all transportation emissions with better home insulation. Are we wasting precious resources by developing infrastructure for rechargeable electric vehicles? Remember that government subsidies are paid for by us. We are not likely to be able to afford reducing electricity grid emissions by 70% for many decades. If we want to green the planet, resources spent on long range REVs simply delay the process. We can have more fun with fast, long range REVs but pay for it with life span reductions. Hmmmmm!

I was surprised to learn from the article that the lithium air battery was originally developed in the 1970's. I'm thinking its not likely to be a success if its taken that long.

This article really makes me question the whole logic of the electric car. All this effort to develop a vehicle that ultimately has lower range, a higher cost, long refueling times, and is unreliable in cold weather. Yes I know they're not "emission free" but really, electric vehicles get most of their charge from coal and gas power plants so can we really say they're emission free?

To travel 200+ miles in an electric car is completely unnecessary for over 90% of passenger car travel. Most trips are way under 30 miles.

The selling to Americans of cars they don't need is one of the main reasons that the US consumer 1) is in hock to there neck, 2) waste more gas/capita than any other major country in the world, and 3) live a great % of their life in traffic.

Look the the SUV and trucks Americans drive. THe vast majority never see a dirt road or ever haul a heavy load. Yet suburban housewives drive these gas guzzling behemoths to malls and soccer games. A complete waste.

Most car trips could easily be done with a 50 mile range electric car. That is what the discussion of alternatives to the combustion engine should concentrate on, no a direct competition to Amercan's muscle car fantasies.